As Kojak says it's way too early to think about ferries for next year Buzzy. By mid May there
should be at least one ferry every day but there are no guarantees.
If you're happy to have an overnight in Rhodes then there should be no problem whichever day you choose since you won't be constrained by flight arrival times and can relax at your hotel until it's time for the ferry.
The best and most up to date information about travel to Symi, including the current ferry woes, is Andy Ward's travel blog at:
Good luck with planning your trip.